weird noise from W124

[wilf1227]

I have a 1992 124 300e petrol. It is the best car I have ever had. It is such a quiet car and having had it for four years I feel I "know" my car. Recently a very strange noise has started. From 20mph and above in any gear (autobox), even if I put into neutral, there is what I can best describe as a reciprocating/whoosh noise. The noise doesn't increase with speed and at higher speeds cannot be heard due to road noise etc. If I drop below 20mph the noise stops. You cannot replicate the noise by increasing the revs either at standstill or when travelling. It doesn't change if you apply the brakes or handbrake, steering lock to lock or when slowing with no throttle applied. At first I thought it was an induction noise or from the air vents. You cannot hear it if you open a window. It seems less pronounced if you apply more throttle. The multi v belt does squeal very occasionally from very cold starts. It is driving me mad as I have to have the radio on to drown it out. Has anyone any ideas at all?

 

[kth286]

As the poly belt squeals at start, perhaps one of the pulleys are
getting stiff due to partial seizing.

The idler pulley bearing can go bad.

Why not remove the poly belt (noting route first, so enabling easy refit)
and turn/pull each pulley to test for roughness/wobble.